Reduced spray intervals to control soybean rust in Brazil

The battle against soybean rust has cost Brazilian farmers billions of dollars since the disease was first discovered in Brazil during the 2000/01 growing season. Improved control methods have paid off in recent years as the disease has been generally kept in check. Those control methods though are now becoming less effective as the disease develops resistance to many of the traditional fungicides.

As a result, the Technical Commission for the Reevaluation of Fungicides in the Brazilian Ministry of Agriculture is now recommending that the interval between fungicide applications be reduced from the current 21 days to 14 days and that farmers only use fungicides that have been proven to be effective against the disease.

The commission, which is composed of scientists from both the government and industry, as well as soybean producers and environmentalists, found that an interval of 21 days was no longer adequately controlling the disease due to the resistance developed by the disease. The new recommendation of spraying every 14 days may increase control costs, but if farmers use one of the 26 fungicides now recommended by the commission, the shorter interval will result in better control.

These recommendations came after an exhaustive review of over 100 fungicide products on the market. The commission removed over 75% of the fungicides from the recommended list because they were no longer effective in controlling the disease. They are now recommending only the 26 fungicide products that proved effective against the disease.

Scientists have been very concerned about the disease developing resistance and they have been recommending that farmers rotate their fungicides with only recommended products that have different modes of action. Continuous applications of only one fungicide allows the disease to quickly develop resistance. Soybean rust is the most serious disease in soybeans and if left uncontrolled, yield losses can be as high as 80%.